1. Field of the Invention
The present invention relates generally to electric railway trucks and more particularly to current collector beams for electric railway trucks incorporating swing arm primary suspensions.
2. Description of the Related Art
Self propelled electric railway trucks require a means to transmit remotely generated power from a trackside third rail to the truck mounted traction motors. One conventional means to accomplish this transfer is through the use of a current collector mounted to the railway truck. The current collector incorporates a shoe or paddle which runs against the electrically charged trackside third rail, which is usually mounted near ground level outboard of the running rails. The electric current from the electrically charged third rail travels from the shoe or paddle of the current collector to the traction motors.
It is highly desirable to minimize the relative motions between the current collector and the electrically charged third rail to insure the proper spatial relationship with the third rail. To achieve this proper relationship with the third rail, it is often desirable to mount the current collector on an unsprung truck member below the primary suspension. This is traditionally accomplished by extending a current collector beam longitudinally between the axle housings on each end of the truck. The current collector is typically fastened to the beam near the truck center line. The beam, constructed of a non-conductive material such as wood or plastic, provides electrical isolation between the current collector and the grounded truck structure.
Relative motions between the axles on opposite ends of the truck create both linear and angular motions between the current collector beam and the axle housing to which it is mounted. On trucks equipped with conventional primary suspensions the axle housing is restrained in a vertically upright alignment throughout the range of vertical, lateral and longitudinal motions. Under these conditions the range of linear and angular motions between the current collector beam and the axle housings are small enough to be accommodated with a simple elastomeric cushion at each end of the beam.
However, on trucks equipped with a swing arm primary suspension, a simple elastomeric cushion at each end of the beam will not suffice because of the presence of additional dynamic motions not encountered with conventional primary suspensions. With the swing arm primary suspension, the axle housing has an arm extending longitudinally inward toward the truck centerline and rotatably fixed to the truck frame via a pivot. The primary springs are located between the swing arm axle housing and the truck frame. In this arrangement, vertical deflection of the primary springs describes an arcuate motion of the axle about the swing arm pivot. Thus, a current collector beam to be used on a swing arm primary suspension must be able to accommodate the larger angular and longitudinal motions created by the arcuate motion in addition to the usual vertical, lateral and longitudinal motions incurred with conventional suspensions.